On-chip high Q inductor

ABSTRACT

A high-Q on-chip inductor includes a primary winding and an auxiliary winding. The primary winding includes a first node and a second node. The auxiliary winding is operably coupled to increase a quality factor of the primary winding.

This patent is claiming priority under 35 USC § 120 as a continuationpatent application to patent application entitled HIGH Q ON-CHIPINDUCTOR AND METHOD OF MANUFACTURE THEREOF, having a serial number ofSer. No. 10/087,614, and a filing date of Mar. 1, 2002 now U.S. Pat. No.6,809,623.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to integrated circuits and moreparticularly to on-chip inductors.

BACKGROUND OF THE INVENTION

As is known, wireless communications standards place stringentrequirements on a wireless communication device's dynamic range ofoperation because the signal strength of received signals may vary bymany orders of magnitude. To meet these requirements, wirelesscommunication devices are designed using radio frequency (RF) integratedcircuits (IC) that consume low power and produce little noise. As isalso known, on-chip inductors are significant components of RFintegrated circuits and are used in oscillators, impedance matchingnetworks, emitter degeneration circuits, filters, and/or baluns. Thus,it is desirable to use on-chip inductors that consume as little power aspossible and produce as little noise as possible.

As is further known, inductor performance is expressed as a qualityfactor (Q-factor), which is associated with the resonance of theinductor and describes both the ability of the inductor to produce alarge output at the resonant frequency and the selectivity (i.e., thepower ratio in decibels versus frequency) of the inductor. As such, theQ-factor is a key component in determining power dissipation and phasenoise of integrated circuits. In general, inductors having a highQ-factor dissipate less power and thus improve the achievable gain.Further, high Q inductors allow an oscillating circuit to perform withminimal power injection from the driving transistor and hence minimizenoise.

In addition, high Q inductors minimize the power leaking into adjacentchannels that corrupts a receiver performance in nearby channels ofcommunication chips, which degrade a receiver's sensitivity.Furthermore, higher dynamic range of wireless communication devices isobtained due to the intrinsic linearity of passive devices.

Not surprisingly, high Q inductors are a key element for RF integratedcircuits to have low power consumption and to achieve the desired noiseperformance. While performance of wireless communication devices is acritical design issue it is typically balanced with manufacturing costsof the devices.

As is known, CMOS technology is widely used for cost effectivefabrication of integrated circuits, including RF integrated circuits.However, on-chip inductors using CMOS technology are known to have amodest quality factor in the range of 5 to 10, which limit theirusefulness is applications that require a high Q inductor, includingsome wireless communication applications.

Therefore, needs exist for a high quality factor on-chip inductor foruse in many applications including wireless communication applications.

SUMMARY OF THE INVENTION

The high Q on-chip inductor of the present invention substantially meetsthese needs and others. In one embodiment, a high-Q on-chip inductorincludes a primary winding and an auxiliary winding. The primary windingincludes a first node and a second node. The auxiliary winding isoperably coupled to increase a quality factor of the primary winding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic block diagram of a high Q on-chipinductor in accordance with the present invention;

FIGS. 2A and 2B illustrate a top and side view of an on-chip inductor inaccordance with the present invention;

FIGS. 3A and 3B illustrate a top and side view of an altering embodimentof an on-chip inductor in accordance with the present invention;

FIGS. 4A, 4B and 4C illustrate another embodiment of an on-chip inductorin accordance with the present invention;

FIGS. 5A, 5B and 5C illustrate yet another embodiment of an on-chipinductor in accordance with the present invention;

FIGS. 6A and 6B illustrate a further embodiment of an on-chip inductorin accordance with the present invention; and

FIG. 7 illustrates a logic diagram of a method for manufacturing anon-chip inductor in accordance with the present invention.

DETAIL DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates a schematic block diagram of a high Q (i.e., qualityfactor) on-chip inductor 10 that includes a primary winding 12 and anauxiliary winding 14, which may be fabricated using CMOS technology,gallium arsenide technology, silicon germanium technology, or any othertype of integrated circuit technology. The primary winding 12 includes a1^(st) node 16 and a 2^(nd) node 18. The auxiliary winding 14 includes a1^(st) node 20 and a 2^(nd) node 22. As shown, the 2^(nd) node 18 ofprimary winding 12 is coupled to the 2^(nd) node 22 of the auxiliarywinding 14. The 1^(st) node 16 and 2^(nd) node 18 of primary winding 12are operably coupled to receive a 1^(st) leg 26 and 2^(nd) leg 28 of aninput 24, respectively. As such, a current (I_(PRI)) flows through theprimary winding 12 based on the magnitude of the input 24 imposed acrossthe 1^(st) node 16 and 2^(nd) node 18 and the inductance value of theprimary winding. As one of average skill in the art will appreciate, theinput 24 may be a voltage input or a current input.

The 1^(st) node 20 of auxiliary winding 14 is operably coupled toreceive a proportionally opposite representation 30 of the 1^(st) leg 26of input 24 (i.e., is reversed biased with respect to the primarywinding). As such, the auxiliary winding 14 has a current (I_(AUX)) thatis proportionally opposite to the current through the primary winding12. If the proportionally opposite representation 30 is of the samemagnitude as the 1^(st) leg of input 24 and the auxiliary winding 14includes the same number of turns as primary winding 12, the auxiliarycurrent will have the same magnitude as the primary current. As one ofaverage skill in the art will appreciate, by scaling the magnitude ofthe proportionally opposite representation 30 and/or by changing thenumber of turns in the auxiliary winding 14 with respect to the numberof turns in primary winding 12, the auxiliary current may be greaterthan or less than the primary current.

As configured, the auxiliary winding 14 is asymmetrical with respect tothe primary winding 12 and has a greater real part admittance (i.e., theinverse of impedance of the winding at an operating frequency) than thereal part of the admittance of the primary winding 12. The asymmetrybetween the primary winding 12 and auxiliary winding 14 may be achievedby one or more of: asymmetrical electromagnetic coupling between theprimary winding and auxiliary winding; an asymmetrical number of turnsbetween the primary winding and auxiliary winding; an asymmetricalgeometric configuration of the primary and auxiliary windings.

The admittances of both the primary winding 12 and auxiliary winding 14include self-admittance and coupled-admittance. The magnitude of theadmittances is dependent on the proximal location of the auxiliarywinding to the primary winding and the asymmetry between the windings.Accordingly, the more closely coupled the auxiliary winding 14 is to theprimary winding 12 and the more asymmetrical the windings are, thegreater the difference will be in the real parts of the admittances ofthe primary winding 12 and the auxiliary winding 14. Such a differenceeffectively decreases the real part of the primary winding's admittanceat an operating frequency (e.g., 2.5 gigahertz to 6 gigahertz), whichincreases the quality factor of the primary winding. For example, theprimary winding 12 may have a quality factor of at least 30 using CMOStechnology.

As one of average skill in the art will appreciate, the high qualityfactor on-chip inductor 10 may be a differential inductor having animbalanced differential input, wherein one half of the differentialinductor functions as the primary winding and the other half functionsas the auxiliary winding.

FIGS. 2A and 2B illustrate a top and side view of the high Q on-chipinductor 10. As shown, the primary winding 12 and auxiliary winding 14are deposited and/or etched on dielectric layer 40. The 2^(nd) node ofprimary winding 12 is operably coupled to the 2^(nd) node of auxiliarywinding 14 via a bridge 42. The bridge may be formed on a 2^(nd)dielectric layer 44. In this configuration, the asymmetrical coupling ofthe auxiliary winding 14 to the primary winding 12 creates at least apart of the asymmetry between the admittance of the windings 12 and 14.

FIGS. 3A and 3B illustrate a top and side view of a high Q on-chipinductor that includes a multi-layered and multi-winding primary winding12 and auxiliary winding 14. As shown in this configuration, the primarywinding 12 includes a plurality of windings, which may have one or moreturns, on multiple dielectric layers. As shown, the primary windingincludes three layers of one turn, on dielectric layer 40, dielectriclayer 44 and dielectric layer 46. Dielectric layer 48 supports bridge42, which couples the primary winding 12 to auxiliary winding 14. Inthis instance, the asymmetry is generated not only by reversed biasedelectromagnetic coupling but also by an asymmetry in the number of turnsbetween the primary and secondary windings. As one of average skill inthe art will appreciate, the primary winding 12 may have one or moreturns on each of the dielectric layers. In addition, the number ofdielectric layers and/or turns may vary from those illustrated in FIGS.3A and 3B.

FIGS. 4A, B, and C illustrate an alternate embodiment of an on-chipinductor that includes the primary winding 12 on dielectric layer 40 andauxiliary winding 14 on a 2^(nd) dielectric layer 44. In this instance,the electromagnetic coupling between the auxiliary winding 14 andprimary winding 12 is increased. Such an increase in reverse biasedelectromagnetic coupling, increases the asymmetry, and thus increasesthe quality factor of primary winding 12. Note that the primary winding12 and auxiliary winding 14 may each include one or more turns and maybe implemented on one or more layers.

FIGS. 5A through 5C illustrate a top, side and bottom view of anotheralternate embodiment of a high Q on-chip inductor. In this illustration,the primary winding 12 includes multiple turns on dielectric layer 40.On dielectric layer 54, metal bridges 52 are placed to provide couplingwithin the primary winding 12. The auxiliary winding 14 is on dielectriclayer 44. As such, the asymmetry is at least partially achieved via thediffering number of turns as well as the reversed biased electromagneticcoupling. As one of average skill in the art will appreciate, theprimary winding may include more or less turns than shown in FIG. 5A andmay be included on one or more layers. In addition, the auxiliarywinding 14 may include more than one turn and may be implemented on morethan one dielectric layer.

FIGS. 6A and 6B illustrate yet another alternate embodiment of a high Qon-chip inductor. In this embodiment, the primary winding 12 andauxiliary winding 14 are on dielectric layer 40. The bridge 42 connectsthe primary winding 12 to the auxiliary winding 14. In this embodiment,underneath dielectric layer 44 is a poly-silicon shield 56. Thepoly-silicon shield 56 is configured in a stacked geometry and furtherincreases the quality factor. For example, in one embodiment of anon-chip inductor using CMOS technology, the quality factor may beincreased to as much as 150. As one of average skill in the art willappreciate, the number of turns of the primary windings 12 and of theauxiliary windings 14 may vary from the one turn as shown in FIGS. 6Aand 6B. In addition, the number of layers used to implement the primarywinding 12 and/or auxiliary winding 14 may vary from the one shown inFIGS. 6A and 6B.

FIG. 7 illustrates a logic diagram of a method of manufacturing a highquality on-chip inductor. The process begins at Step 60 where a primarywinding is created to have a 1^(st) admittance and to include a 1^(st)and 2^(nd) node on a dielectric layer. The creation of the primarywinding may be done by depositing, etching and/or any other method forobtaining a metal layer on a dielectric layer in an integrated circuitfabrication process. The process then proceeds to Step 62 whereauxiliary winding is created to have a 2^(nd) admittance and to includea 1^(st) and 2^(nd) node. The 2^(nd) node of the primary winding iscoupled to the 2^(nd) node of the auxiliary winding. In addition, thecreation of the real part of the 2^(nd) admittance is done to be greaterthan the real part of the admittance of the primary winding. The primarywinding is operably coupled to receive an input, while the auxiliarywinding is operably coupled to receive a proportionally oppositerepresentation of the input.

The admittance of the primary winding includes both self-admittance andcoupled-admittance. Similarly, the admittance of the auxiliary windingincludes self-admittance and coupled-admittance. The difference in thereal parts of the admittance of both windings is dependent on theproximal location of the auxiliary winding to the primary winding andthe asymmetry between the windings. The greater the coupling andasymmetry between the auxiliary winding and primary winding, the lowerthe real portion of the primary winding admittance will be, thusincreasing the quality factor for the primary winding.

The asymmetry between the auxiliary winding the primary winding may bedone by asymmetrical electrical coupling between the primary winding andauxiliary winding, differing number of turns in the primary windingversus the number of turns in the auxiliary winding, and/or by creatingthe primary winding to have a different geometric configuration thanthat of the auxiliary winding.

The quality factor of the primary winding may be enhanced by creating apoly-silicon shield that is operably coupled to the primary winding andthe auxiliary winding. As one of average skill in the art willappreciate, the primary winding and/or auxiliary winding may be createdto have multiple turns on multiple layers and/or a single turn on asingle layer and/or any combination thereof.

The preceding discussion has presented a high quality on-chip inductor.Such a high quality on-chip inductor dramatically increases the qualityfactor of inductors thus making it very applicable for a wide variety ofcircuit applications including radio frequency integrated circuits,on-chip filters, et cetera. As one of average skill in the art willappreciate, other embodiments may be derived from the teachings of thepresent invention, without deviating from the scope of the claims.

1. A high-Q on-chip inductor comprises: primary winding including afirst node and a second node, wherein the first node receives an firstinput signal; and auxiliary winding operably coupled to the primarywinding to increase a quality factor of the primary winding, wherein theauxiliary winding receives a second input signal that is aproportionally opposite representation of the first input signal andproduces therefrom an auxiliary current that is proportionally oppositeof a current of the primary winding; wherein the first input signal andthe second input signal each comprise one of a voltage input and acurrent input.
 2. The high-Q onchip inductor of claim 1, wherein theauxiliary winding is proximally located to, and reversed biased withrespect to, the primary, winding to at least partially establish anadmittance of the auxiliary winding to be greater than an admittance ofthe primary winding.
 3. The high-Q on-chip inductor of claim 1, whereinthe auxiliary winding is asymmetric with respect to the primary windingto at least partially establish an admittance of the auxiliary windingbeing greater than an admittance of the primary winding.
 4. The high-Qon-chip inductor of claim 3, wherein the asymmetry is achieved by atleast one of: asymmetrical electromagnetic coupling between the primarywinding and the auxiliary winding, asymmetrical number of turns betweenthe primary winding and the auxiliary winding, and asymmetricalgeometric configuration of the primary and auxiliary windings.
 5. Thehigh-Q on-chip inductor of claim 1, further comprises a poly-siliconshield operably coupled to the primary winding and to the auxiliarywinding.
 6. The high-Q on-chip inductor of claim 1 further comprises:the primary winding including a plurality of turns on multipledielectric layers of an integrated circuit, wherein the plurality ofturns are operably coupled via bridges on differing dielectric layers ofthe integrated circuit; and the auxiliary winding including at least oneturn on at least one of the multiple dielectric layers of the integratedcircuit.
 7. The high-Q on-chip inductor of claim 1 further comprises:the primary winding including at least one turn on a first dielectriclayer of an integrated circuit; and the auxiliary winding including atleast one turn on a second dielectric layer of the integrated circuit,wherein the at least one turn of the primary winding is stacked withrespect to the at least one turn of the auxiliary winding.